In an engine or other prime mover with piston or other reciprocating parts, for example, the piston and a cylinder will wear due to relative sliding motions between them, resulting in production of iron powder or other magnetic material entrained in drain oil from the engine flowing through a passage. Thus, it is required to measure a concentration of magnetic material contained in the passage of the drain oil from the engine in order to accurately grasp worn degree of the equipment.
Generally, in order to grasp the worn degree of the equipment, the fluid such as lubricant or drain oil is manually sampled to measure a concentration of magnetic material through chemical technique; alternatively, a device for measuring a concentration of magnetic material is arranged adjacent to the passage of flow of the fluid to measure the concentration of magnetic material.
The device for measuring a concentration of magnetic material comprises, for example, magnetic-field applying means and magnetic measurement means with a magnetic sensor in the form of a superconducting quantum interference device both arranged adjacent to the passage of flow of the fluid such as drain oil so as to detect only magnetic fields of magnetized components. This has been disclosed for example in Patent Literature 1. Another example comprises an observational LC oscillation circuit with a first coil adjacent to the passage of the fluid and a corrective LC oscillation circuit with a second coil arranged in a position not affected by magnetic material in the fluid, the concentration of magnetic material being detected on the basis of difference in oscillating frequency between the observation and corrective LC oscillation circuits. This has been disclosed for example in Patent Literature 2.    [Patent Literature 1] JP10-268013A    [Patent Literature 2] JP2005-83897A